Sloth Miniscus Probably Megalonyx
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COMMENT: this is a crescent shaped fibrocartilaginous structure that usually does not fossilize. Often present in joint cavities, in this case probably the knee, it strengthens the joint when it undergoes tension and torsion. These are quite rare and the only ones we have seen.
Sloths belong to the group called Xenarthrans, formerly called Edentata, including anteaters, glyptodonts, armadillos and sloths. Those from Florida evolved in South America. Most fossil xenarthrans have no enamel on their teeth, but the teeth continued to grow throughout the life of the animal so as to compensate for this. There were basically three different types or genus of sloths in Florida, the mylodontids, the megalonychids, and the megatheres. The first includes the Thinobastides in the Miocene, and the small Glossotherium chapadmalense and the larger Paramylodon harlani. These are ones which have the straight, more rounded in cross-section claw cores.
The second group are the megalonychids which arrived in the late Miocene and lasted until the late Pleistocene. These start with the Pliometanastes and grow progressively larger through M. curvidens, (early Pliocene), leptostomus, (late Pliocene-early Pleistocene) M. wheatleyi, and M. jeffersonii. These sloths had more curved, flat claw cores, as did the eremotheres. In the teeth that follow, the smaller teeth are those of the earlier sloths.
The third type includes the enormous eremothere, megathere and the much smaller Nothrotheriops texanum. These are relatively more scarce in Florida than the other two types. The large Eremotherium teeth are often found split in half. Indeed, all sloth teeth are fragile and need careful handling.